John Olsen By Colin Barras Humans arrived on the Tibetan Plateau tens of thousands of years earlier than we thought. This raises the possibility that the first humans to cope with the harsh conditions there were not modern humans, but the ancient Denisovans. The Tibetan Plateau is a tough environment. The average annual temperature is close to 0 °C, and on average it’s 4000 metres above sea level so the air is difficult to breathe. Most researchers assumed that humans didn’t move onto the Tibetan Plateau until just 12,000 years ago – and only occupied it permanently about 3600 years ago. An archaeological site called Nwya Devu suggests otherwise. The site, which is on the Tibetan Plateau 4600 metres above sea level, has yielded thousands of stone tools, albeit few organic remains. By using technology that establishes how many years have passed since the soil burying the tools was last exposed, archaeologists estimate that the oldest tools are between 40,000 and 30,000 years old. That means humans first occupied the Tibetan Plateau much earlier than we thought. Xing Gao An extraordinary theory might explain how humans adapted to life so high above sea level. Most Tibetans carry an unusual stretch of DNA in their genomes, which they seem to have gained when modern humans bred with an ancient group of humans called the Denisovans. The Denisovan DNA seems to help Tibetans cope with the limited oxygen supply at altitude. A 2014 study suggested the Denisovan DNA became more common in the ancestors of today’s Tibetans between about 40,000 and 30,000 years ago, again hinting that modern humans were on the Tibetan Plateau by 30,000 years ago. But there is an alternative scenario, says John Olsen at the University of Arizona in Tucson, a member of the Nwya Devu excavation team. If modern humans harnessed Denisovan DNA to survive at altitude, perhaps the Denisovans could also survive on the Tibetan Plateau. There are no human remains at Nwya Devu and Olsen says attempts to extract human DNA from the sediment have so far failed. But he says the stone tools might be the handiwork of Denisovans, rather than modern humans. “What we know is that the Denisovans left their homeland in the Altai Mountains of southern Siberia and eventually trekked all the way to Melanesia [the islands northeast of Australia], taking with them their signature genome,” he says. “One logical route for such a migration may have included passage up and over the Tibetan Plateau.” In line with this, Olsen points out that the stone tools at Nwya Devu are similar to those seen in southern Siberia, where we know the Denisovans lived, and not much like those made by Stone Age humans in China. But without fossil or DNA evidence, Olsen says we can only speculate on the identity of the first Tibetans. Journal reference: Science, DOI: 10.1126/science.aat8824 More on these topics: